Derivative Financial Instruments - Gross and net amounts for OTC derivatives (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Asset derivatives
Asset derivatives gross amount	$ 150	$ 218
Asset derivatives, gross liability	(2)	(12)
Derivative assets net amount on balance sheet	148	206
Liability derivatives
Liability derivatives gross amount	(589)	(657)
Liability derivatives, gross asset	22	2
Net amount on balance sheet	(567)	(655)
OTC derivatives
Asset derivatives
Asset derivatives gross amount	21	10
Asset derivatives, gross liability	(21)	(9)
Cash collateral received	2	0
Derivative assets net amount on balance sheet	2	1
Derivative assets received under securities collateral	0	0
Derivative asset, fair value, amount offset against collateral	2	1
Liability derivatives
Liability derivatives gross amount	(9)	(19)
Liability derivatives, gross asset	21	9
Derivative liability offsets under cash collateral pledged	(20)	9
Net amount on balance sheet	(8)	(1)
Derivative liabilities received under securities collateral	0	0
Derivative liability, fair value, amount offset against collateral	$ (8)	$ (1)